Sputtering is known in the art as a technique for depositing onto substrates. For example, antireflective (AR), transparent conductive, and/or low-emissivity (low-E) coatings can be deposited onto a glass substrate by successively sputter-depositing one or more different layers onto the substrate. As an example, a low-E coating may include in the following order: a glass substrate/SnO2/ZnO/Ag/ZnO, where the Ag layer is an IR reflecting layer and the metal oxide layers are dielectric layers. In this example, one or more tin (Sn) targets may be used to sputter-deposit the base layer of SnO2, one or more zinc (Zn) inclusive targets may be used to sputter-deposit the next layer of ZnO, an Ag target may be used to sputter-deposit the Ag layer, and so forth. As another example, a Ti or TiOx target may be used to sputter-deposit a layer of titanium oxide (e.g., TiOx) on a substrate as a base layer or as some other layer in the stack in certain instances. The sputtering of each target is performed in a chamber housing a gaseous atmosphere (e.g., a mixture of Ar and O gases in the Sn, Ti and/or Zn target atmosphere(s)). In each sputtering chamber, sputtering gas discharge is maintained at a partial pressure less than atmospheric.
Example references discussing sputtering and devices used therefore include U.S. Pat. Nos. 5,427,665, 5,725,746, 6,743,343, and 2004/0163943, the entire disclosures of which are all hereby incorporated herein by reference.
A sputtering target (e.g., cylindrical rotatable magnetron sputtering target) typically includes a cathode tube within which is a magnet array. The cathode tube is often made of stainless steel or some other conductive material. The target material is formed on the tube by spraying, casting or pressing it onto the outer surface of the stainless steel cathode tube (optionally, a backing layer may be provided between the cathode tube and the target material layer). Each sputtering chamber includes one or more targets, and thus includes one or more of these cathode tubes. The cathode tube(s) may be held at a negative potential (e.g., −200 to −1500 V), and may be sputtered, when rotating. Due to the negative biased potential on a target, ions from the sputtering gas discharge are accelerated into the target and dislodge, or sputter off, atoms of the target material. These atoms, in turn, together with the gas form the appropriate compound (e.g., tin oxide) that is directed to the substrate in order to form a thin film or layer of the same on the substrate.
There are different types of sputtering targets, such as planar magnetron and cylindrical rotatable magnetron targets. Planar magnetrons may have an array of magnets arranged in the form of a closed loop and mounted in a fixed position behind the target. A magnetic field in the formed of a closed loop is thus formed in front of the target. This field causes electrons from the discharge to be trapped in the field and travel in a pattern which creates a more intense ionization and higher sputtering rate.
In the case of rotating magnetron sputtering targets, the cathode tube and target material thereon are rotated over a magnetic array (that is often stationary) that defines the sputtering zone. Due to the rotation, different portions of the target are continually presented to the sputtering zone which results in a fairly uniform sputtering of the target material off of the tube.
Materials such as tin oxide, zinc oxide, and silicon nitride have an index of refraction (n) around 2, where SiO2 has an index of refraction (n) of about 1.5 and TiO2 has an index of refraction of about 2.4. There exists a need for materials, that can be used in low-E, transparent conductive, and/or AR coatings, that have an index of refraction (n) between these values (e.g., from about 1.6 to 1.9, or 2.1 to 2.3, for example). Materials with such index values would be advantageous in that they could be used to further reduce reflection in coated articles using low-E and/or AR coatings having the same. Alloys, mixes of reactive gases, or combinations of both alloys and mixtures of reactive gases may be used to generate thin films having desired properties that cannot be achieved using a single elemental metal approach, or a pure oxide approach.
The approach of using alloy metals as metal sputtering targets is limited by achievable small ranges of solid solution that restrict the ratio amount different materials. Metallic alloy metal targets also face low deposition rate problems in reactive sputtering when full oxide and/or nitride films are desired.
The approach of mixing gases when sputtering metal or Si targets is also problematic. Silicon and aluminum oxynitride can be tailored to obtain index values from 1.6 to 1.9. However, unfortunately, the conventional way of doing this is to use a Si or Al target and vary the gas flows of nitrogen and oxygen to gain the desired oxygen to nitrogen ratio in the resulting layer to adjust its index of refraction value. It is difficult to consistently adjust oxygen/nitrogen stoichiometry in the resulting layer in a desired manner by adjusting oxygen and nitrogen gas flows using a Si or Al target. Oxygen and nitrogen gases have different weights and it is difficult to get consistent predictable results by varying oxygen and nitrogen gas flows when using a Si target in sputtering silicon oxynitride. Therefore, layers deposited according to these methods may be difficult to make and/or have inconsistent and/or varying compositions.
In view of the above, it will be appreciated that there exists a need in the art for an improved technique to consistently form sputter-deposited layers having an index of refraction (n) in the range of from about 1.6 to 1.9. In particular, there exists a need for a technique that permits layers to be formed in a manner that allows a desired refraction index value in this range to be consistently achievable. Further, there is a need in the art for the resulting layer.
Certain example embodiments of this invention relate to a layer of or including Ti1-xSixOy and/or a method of making a coated article including such a layer. In certain example embodiments, the layer may be deposited from a rotatable magnetron sputtering target, a stationary planar target, or the like. In certain example embodiments, the Ti1-xSixOy may be substoichiometric with respect to oxygen. However, in other example embodiments, the Ti1-xSixOy based layer may be fully oxidized. In certain example embodiments of this invention, the layer may be of or include Ti1-xSixOy where x is from about 0.05 to 0.95 (more preferably from about 0.1 to 0.9, and even more preferably from about 0.2 to 0.8, and possibly from about 0.5 to 0.8) and y is from about 0.2 to 2 (more preferably from about 1 to 2, and even more preferably from about 1.5 to 2, and possibly from about 1.9 to 2). The layer may be sputter-deposited in an atmosphere of or including one or more of Ar, O2 and/or N2 gas(es) in certain example embodiments of this invention. Other materials may be provided in the target in alternative example embodiments of this invention.
Depositing titanium silicon oxide-inclusive layers from a target including at least silicon and titanium may permit layers with tunable indices of refraction (n) to be consistently achieved by sputter deposition. By adjusting the Ti and Si amounts in the target (e.g., the Ti/Si ratio in the target itself), layers of or including TiSiOx can be formed by sputter-deposition and can achieve consist desired index values (n) (e.g., where n is from about 1.5 to 2.0, or 1.6 to 1.9). For example, the more Si in the target, the lower the index of refraction (n) value of the resulting sputter-deposited layer. Likewise, the more Ti in the target (and thus the less Si), the higher the index of refraction (n) value of the resulting sputter-deposited layer. Thus, an improved technique is provided to consistently form sputter-deposited thin film layers having an index of refraction (n) in the range of from about 1.6 to 1.9. In particular, a technique is provided that permits layers to be sputter-deposited in a manner that allows a desired refraction index (n) value in this range to be consistently achievable. While gas flows may be adjusted to alter or tailor the index (n) value of the resulting layer, the index (n) value of the resulting layer may be adjusted by adjusting the Ti/Si ratio in the target itself.
The combination of Ti and Si in the target is advantageous in that Si and Ti form a suitable alloy. In certain example embodiments, when a ceramic target including Ti and Si is used, the amounts of Ti and Si can be varied to allow the desired index (n) value to be obtained in the resulting layer. Moreover, the ceramic nature of the sputtering target is advantageous in that it permits higher sputtering rates to be achieved. The oxygen in the target is stoichiometric (or close to stoichiometric) in certain example embodiments of this invention. Further, in certain example embodiments, the silicon oxide in the target has a higher sputter rate than the titanium oxide in the target. Therefore, in certain example embodiments, the ratio of Si to Ti in the film will be higher than the ratio of Si to Ti in the target itself In other example embodiments, a titanium silicon oxide-inclusive layer may be formed through use of a metallic target, sputtered in the presence of oxygen and/or other gases.
In certain example embodiments of this invention, there is provided a method for making a coated article, the method comprising sputter-depositing a first medium index layer comprising Ti1-xSixOy on a glass substrate, where x is from about 0.05 to 0.95 and y is from about 0.2 to 1.95, wherein said medium index layer comprising Ti1-xSixOy is sputter-deposited by a target comprising Si and Ti, wherein the ratio of Si to Ti is from about 3:1 to 2:1, forming a high index layer over and contacting the medium index layer; forming a low index layer over and contacting the high index layer; and wherein the medium index layer has an index of refraction of from about 1.6 to 1.9, and a thickness of from about 30 to 70 nm, wherein the high index layer has an index of refraction of from about 2.0 to 2.4, and a thickness of from about 75 to 125 nm, wherein the low index layer has an index of refraction of from about 1.4 to 1.6, and a thickness of from about 65 to 115 nm, and wherein the medium index layer, the high index layer, and the low index layer form an anti-reflective coating.
In certain example embodiments of this invention, there is provided a method of making a coated article, the method comprising: providing a target comprising Si and Ti, wherein the target comprises more Si than Ti (atomically); sputter-depositing a layer comprising Ti1-xSixOy on a substrate by flowing argon and/or oxygen gas in a chamber where the target is located, so as to cause the layer comprising silicon oxide and titanium oxide to be formed on the substrate, where x is greater than about 0.5, and y is less than or equal to 2; forming a layer consisting essentially of titanium oxide over and contacting the layer comprising Ti1-xSixOy; forming a layer consisting essentially of silicon oxide over and contact the layer consisting essentially of titanium oxide; wherein the layer consisting essentially of titanium oxide has an index of refraction that is the higher than that of the layer comprising Ti1-xSixOy, and the layer comprising Ti1-xSixOy has an index of refraction higher than the layer consisting essentially of silicon oxide, and wherein the three layers form an antireflective coating on the glass substrate.
In still further example embodiments of this invention, there is provided a coated article, where the coated article comprises an antireflection coating, wherein the anti-reflection coating comprises: a first layer having a medium index of refraction and comprising Ti1-xSixOy, where x is greater than or equal to 0.5, and having a thickness of from about 30 to 70 nm; a second layer having a comparatively higher index of refraction and comprising an oxide of titanium, and having a thickness of from about 80 to 110 nm; a third layer having an index of refraction lower than both the first and second layers, and comprising an oxide of silicon, having a thickness of from about 70 to 100 nm; and wherein the medium index layer is formed by sputter deposition from a ceramic target comprising a target material comprising titanium, silicon and oxygen, and has an index of refraction of from about 1.6 to 1.9.
In still further example embodiments, there is provided a method for making a coated article, the method comprising: forming a transparent conductive coating on a glass substrate, wherein the transparent conductive coating is formed by: sputter-depositing a layer comprising Ti1-xSixOy on a glass substrate, where x is from about 0.05 to 0.95 and y is from about 1 to 2, wherein said layer comprising Ti1-xSixOy is sputter-deposited by a target comprising Si and Ti; and forming a transparent conductive oxide layer over and contacting the layer comprising Ti1-xSixOy, wherein the TCO layer has a thickness of from about 200 to 400 nm; and wherein the layer comprising Ti1-xSixOy has a thickness of from about 50 to 90 nm, and an index of refraction of from about 1.6 to 1.9.